A variable displacement compressor is used, for example, in a vehicle air-conditioning system. The displacement control of the variable displacement compressor is carried out by opening/closing a displacement control electromagnetic valve.
For example, in the case of the displacement control device using a displacement control electromagnetic valve shown in FIG. 2 of Patent Document 1, current (control current I) supplied to an electromagnetic coil of a solenoid unit is adjusted so that difference between pressure of a discharge chamber of a compressor (discharge pressure Pd) and pressure of a suction chamber (suction pressure Ps) (Pd−Ps differential pressure) becomes a given value.
The displacement control electromagnetic valve has a first compression coil spring that biases a valve body in a valve-opening direction and a second compression coil spring that biases the valve body in a valve-closing direction. The first compression coil spring has a larger biasing force than the second compression coil spring. For that reason, when the control current I is zero, the displacement control electromagnetic valve is in an open position, and discharge displacement is maintained at minimum.